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crypto/sharing/v1/polynomial.go

@@ -0,0 +1,49 @@
+//
+// Copyright Coinbase, Inc. All Rights Reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package v1
+
+import (
+	"github.com/onsonr/hway/crypto/core/curves"
+)
+
+type polynomial struct {
+	Coefficients []*curves.Element
+}
+
+// newPoly creates a random polynomial of the given degree but with the provided intercept value
+func newPoly(intercept *curves.Element, degree uint32) (polynomial, error) {
+	p := polynomial{
+		Coefficients: make([]*curves.Element, degree),
+	}
+
+	// Intercept is the value to be split
+	p.Coefficients[0] = intercept
+
+	// random coefficients
+	for i := uint32(1); i < degree; i++ {
+		c, err := intercept.Field().RandomElement(nil)
+		if err != nil {
+			return p, err
+		}
+		p.Coefficients[i] = c
+	}
+
+	return p, nil
+}
+
+// evaluate returns the value of the polynomial for the given x
+func (p polynomial) evaluate(x *curves.Element) *curves.Element {
+	// Compute the polynomial value using Horner's Method
+
+	degree := len(p.Coefficients) - 1
+	result := p.Coefficients[degree].Clone()
+	for i := degree - 1; i >= 0; i-- {
+		result = result.Mul(x).Add(p.Coefficients[i])
+	}
+
+	return result
+}